How new is she? Do you know how old she is? Did you quarantine for any period?
Any time birds are moved to new ground they can be exposed to previously unexposed to strains of coccidia, so coccidiosis has to be considered. Young birds are more at risk. Have you seen any droppings from her, what do they look like? Sitting hunched/fluffed up, lethargy, going off food and water, runny, mucousy, or bloody droppings are all symptoms. I would get some Corid and treat for coccidiosis.
Dose is 1.5 tsp of the powder per gallon of water, or 2 tsp of the liquid per gallon of water for 5-7 days. Medicated water has to be the only water available during treatment. Make it fresh daily. You can also give her an oral dose every day for up to three days in addition to the medicated water, dosing for that is here:
https://www.backyardchickens.com/threads/corid-oral-drench-instructions.1211991/
If she is not drinking well on her own then you can give her the regular medicated water orally several times a day until she does start drinking.
Corid is available at
Tractor Supply stores and many feed stores, in the livestock section.
